The present invention relates generally to a method for determining parameters which are to be used in designing a hydraulic fracturing treatment of an underground formation.
Methods of calculating certain parameters used in fracture treatment designs have been used through the years either to check assumptions made during design or to measure parameters to be used in design. One method commonly used to gather such information is the pump-in, shut-in mini-frac test where fluid is injected at a constant rate for a set period of time and then injection is immediately shut in. The downhole pressures are measured during the shut-in period and then are used to determine various parameters.
While these pump-in, shut-in tests have proved valuable in the past, they suffer from several shortcomings including (1) the analysis is dependent on accurate knowledge of rock properties, (2) the analysis is often dependent on accurate knowledge of fluid flow properties, (3) the pressure drop acting as a driving force for fluid loss changes with time, (4) the analysis require the assumption of a fracture height, and (5) the analysis is greatly dependent on the selection of a fracture width equation. The most critical of these shortcomings is the need to assume the applicability of a particular fracture width equation.
None of the current methods, i.e., Nolte, U.S. Pat. No. 4,398,416, and Lee, U.S. Pat. No. 4,848,461, eliminate the need for either knowledge of, or an assumption of, formation data, including the plane-strain modulus, E'. Current methods are heavily dependent on the three fracture geometry models widely known in the industry. In addition, any one of the current methods requires the assumption of a fracture height. While, when using one of the current methods, the fluid-loss exponent may be determined by methods introduced in U.S. Pat. No. 5,005,643 "Method of Determining Fracture Parameters for Heterogeneous Formations" by Mohamed Y. Soliman et al., those methods still suffer from the need for knowledge of, or assumptions of, formation data. As a result, because of the assumptions made in the known methods the actual fracture design starts with a potential for error.